During the production of grinding wheels for example, the article is fired in order to melt some of the components and form the final article. This melting increases the strength of the article and disadvantageously causes the structure to be consolidated which results in shrinkage of the article. It is generally desirable to reduce grinding forces caused by a grinding wheel by having a more open structure which refers to a lower percentage of abrasive. However, a lower percentage of abrasive will further increase the consolidation of the structure during firing. This additional shrinkage reduces the volume of the abrasive article and thereby causes the percent of the abrasive in the final article to be much higher than in the “green” article, and therefore defeats the purpose of reducing the amount of abrasive. Therefore, methods of reducing shrinkage are constantly being sought.
Fugitive pore inducers, such as walnut shells, are widely used to encourage an open structure, but these have the effect of leaving a void behind after the fugitive pore inducer has burnt out or evaporated. This void is then partially collapsed during the sintering shrinkage. This partially defeats the purpose of including the pore inducer.
Providing a secondary abrasive in addition to the primary abrasive will reduce sintering shrinkage. However, this approach adds the disadvantage that the high hardness of the abrasive fillers will lead to increased grinding forces during use, as the secondary abrasive filler will not abrade away as would a softer filler. Therefore, this approach again defeats the purpose.
Therefore, there remains a need for methods of reducing shrinkage of sintered abrasive articles that do not add undesirable characteristics to the final article.